U.S. patent application number 11/345181 was filed with the patent office on 2007-08-02 for method and system for identifying signal frequencies emitted at a known location using geographically distributed rf sensors.
Invention is credited to Mutsuya Ii.
Application Number | 20070178844 11/345181 |
Document ID | / |
Family ID | 38322720 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070178844 |
Kind Code |
A1 |
Ii; Mutsuya |
August 2, 2007 |
Method and system for identifying signal frequencies emitted at a
known location using geographically distributed RF sensors
Abstract
A network of three or more RF sensors acquires RF data in terms
of power versus frequency data or energy versus frequency data. An
expected power or energy difference between RF sensors in each pair
of RF sensors is calculated based on the known location. The
observed power or energy differences are then compared with the
expected differences to determine whether the expected and observed
differences match or nearly match for one or more particular
frequencies. When the observed and expected differences match or
nearly match, the particular frequency is determined to be a
probable frequency for the RF signal emitted at the known
location.
Inventors: |
Ii; Mutsuya; (Shoreline,
WA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES INC.
INTELLECTUAL PROPERTY ADMINISTRATION,LEGAL DEPT.
MS BLDG. E P.O. BOX 7599
LOVELAND
CO
80537
US
|
Family ID: |
38322720 |
Appl. No.: |
11/345181 |
Filed: |
January 31, 2006 |
Current U.S.
Class: |
455/67.11 |
Current CPC
Class: |
G01S 5/0252 20130101;
H04B 17/382 20150115 |
Class at
Publication: |
455/067.11 |
International
Class: |
H04B 17/00 20060101
H04B017/00 |
Claims
1. A method for identifying one or more probable signal frequencies
for an RF signal emitted at a known location using geographically
distributed RF sensors, comprising: calculating an expected signal
value difference between RF sensors in each pair of RF sensors
based on the known location; acquiring RF data over a given
frequency spectrum; and comparing observed signal value differences
with the expected signal value differences over the given frequency
spectrum.
2. The method of claim 1, further comprising: determining whether
one observed signal value difference substantially matches one
expected signal value difference for one pair of sensors; and
repeatedly determining whether one observed signal value difference
substantially matches one expected signal value difference for the
remaining pairs of sensors.
3. The method of claim 2, further comprising determining the one or
more probable signal frequencies of the RF signal when the observed
signal value differences substantially match the expected signal
value differences.
4. The method of claim 1, further comprising: each RF sensor
generating a spectral trace of the acquired RF data; transmitting
the spectral traces over a network connection; and storing the
spectral traces in a central processing device connected to the RF
sensors.
5. The method of claim 1, wherein the signal value differences
comprise power differences.
6. The method of claim 1, wherein the signal value differences
comprise energy differences.
7. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
comparing power versus frequency graphs associated with the RF
sensors.
8. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
comparing amplitude versus frequency graphs associated with the RF
sensors.
9. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
generating a table comprised of energy differences.
10. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
generating a table comprised of power differences.
11. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
generating a table comprised of energy levels.
12. The method of claim 1, wherein comparing observed signal value
differences with the expected signal value differences comprises
generating a table comprised of power levels.
13. The method of claim 1, further comprising outputting the one or
more probable signal frequencies.
14. The method of claim 1, further comprising storing the one or
more probable signal frequencies.
15. A system for identifying one or more probable signal
frequencies for an RF signal emitted at a known location,
comprising: a central processing device; and a plurality of RF
sensors each connected to the central processing device through a
network connection, wherein each RF sensor is operable to acquire
signal value versus frequency data for acquired RF data and
transmit the signal value versus frequency data to the central
processing device using the network connection, wherein the central
processing device determines the one or more probable signal
frequencies using the received signal value versus frequency
data.
16. The system of claim 15, wherein the signal value versus
frequency data comprises power versus frequency data.
17. The system of claim 15, wherein the signal value versus
frequency data comprises amplitude versus frequency data.
18. The system of claim 15, wherein the central processing device
comprises a discrete computing device.
19. The system of claim 15, wherein the central processing device
is integrated within one RF sensor in the plurality of RF
sensor.
20. The system of claim 15, wherein the central processing device
comprises an output device and a memory.
Description
BACKGROUND
[0001] RF signals are used in a variety of applications, such as
medical imaging, broadcast radio, and wireless communications. It
is often desirable to determine if an RF signal is present, and if
so, the location of the signal emitter. For example, the
transmission of an RF signal may be detected as part of a criminal
investigation, or to detect and locate unauthorized or
unintentional transmissions.
[0002] FIG. 1 is a conceptual diagram of a system for geolocating
an RF signal emitter in accordance with the prior art. An RF signal
is received by RF sensor system 100. To determine the location of
the emitter transmitting the RF signal, three or more RF sensors in
system 100 receive the RF signal. The location of the emitter is
determined using one of several known techniques, such as
time-difference-of-arrival.
SUMMARY
[0003] In accordance with the invention, a method and system for
identifying signal frequencies emitted at a known location using
geographically distributed RF sensors are provided. A network of
three or more RF sensors acquires RF data in terms of power versus
frequency data or energy versus frequency data. An expected power
or energy difference between RF sensors in each pair of RF sensors
is calculated based on the known location. The observed power or
energy differences are then compared with the expected differences
to determine whether the expected and observed differences match or
nearly match for one or more particular frequencies. When the
observed and expected differences match or nearly match, the
particular frequency is determined to be a probable frequency for
the RF signal emitted at the known location.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a conceptual diagram of a system for geolocating
an RF signal emitter in accordance with the prior art;
[0005] FIG. 2 is a conceptual diagram of a system for identifying
one or more signal frequencies in an embodiment in accordance with
the invention;
[0006] FIG. 3 is a block diagram of system 200 in FIG. 2 in an
embodiment in accordance with the invention;
[0007] FIG. 4 is a flowchart of a method for identifying one or
more signal frequencies emitted at a known location in an
embodiment in accordance with the invention;
[0008] FIGS. 5A-5B depict a flowchart of a method for identifying
and monitoring one or more signal frequencies emitted at a known
location in an embodiment in accordance with the invention;
[0009] FIG. 6A is an illustration of a first table that may be used
in block 410 of FIG. 4 and block 514 of FIG. 5B;
[0010] FIG. 6B is an illustration of a second table that may be
used in block 410 of FIG. 4 and block 514 of FIG. 5B; and
[0011] FIG. 7 is a pictorial representation of two traces of the
power of an RF signal over a frequency spectrum that may be used in
block 410 of FIG. 4 and in block 514 of FIG. 5B.
DETAILED DESCRIPTION
[0012] The following description is presented to enable embodiments
in accordance with the invention to be made and used, and is
provided in the context of a patent application and its
requirements. Various modifications to the disclosed embodiments
will be readily apparent, and the generic principles herein may be
applied to other embodiments. Thus, the invention is not intended
to be limited to the embodiments shown, but is to be accorded the
widest scope consistent with the appended claims and with the
principles and features described herein.
[0013] With reference to the figures and in particular with
reference to FIG. 2, there is shown a conceptual diagram of a
system for identifying one or more signal frequencies in an
embodiment in accordance with the invention. System 200 determines
one or more probable frequencies for an RF signal emitted at a
given location. Unlike the system of FIG. 1, which determines a
location using received RF signals, the system shown in FIG. 2
determines probable signal frequencies for RF signals using
expected energy or power ratios determined for the known
location.
[0014] FIG. 3 is a block diagram of system 200 in FIG. 2 in an
embodiment in accordance with the invention. System 200 is a
network of RF sensors arranged in any given topology in embodiments
in accordance with the invention. System 200 includes RF sensors
300, 302, 304, central processing device 306, and common network
clock 308 each connected through network connection 310. Network
connection 310 is implemented as a wired connection in an
embodiment in accordance with the invention. For example, network
200 is a wired local area network (LAN) in an embodiment in
accordance with the invention. In other embodiments in accordance
with the invention, network connection 310 is implemented as a
wireless connection, such as a wireless local area network (WLAN),
or as a combination of both wired and wireless connections.
[0015] Central processing device 306 includes output device 312,
processor 314, memory 316, and database 318. Central processing
device 306 is implemented as a discrete processing device, such as
a computer, in an embodiment in accordance with the invention. In
another embodiment in accordance with the invention, central
processing device 306 is integrated within an RF sensor in network
200.
[0016] RF sensors 300, 302, 304 are implemented as any device that
captures RF data in terms of power versus frequency or amplitude
versus frequency. One example of such an RF sensor is a spectrum
analyzer. RF sensors 300, 302, 304 transmit the data to central
processing device 306 in an embodiment in accordance with the
invention. Processor 314 determines one or more probable signal
frequencies using the received data. Output device 312 then outputs
the probable frequency or frequencies to a user. Output device 312
is implemented, for example, as a display or printing device. In
other embodiments in accordance with the invention, the probable
frequency or frequencies are stored in memory 316. And in yet
another embodiment in accordance with the invention, database 318
stores spectral traces received from multiple RF sensors. The
spectral traces are then used to determine the probable frequency
or frequencies emitted at one or more locations.
[0017] Central processing device 306 and RF sensors 300, 302, 304
also exchange timing information that is used to synchronize RF
sensors 300, 302, 304 to a common time defined by common network
clock 308. Common network clock 308 is integrated within central
processing device 306 or within an RF sensor in network 200 in an
embodiment in accordance with the invention. RF sensors 300, 302,
304 acquire RF data over the same period of time when the sensors
are synchronized to a common network time.
[0018] Network 200 uses the Institute of Electrical and Electronic
Engineers (IEEE) 1588 Standard to synchronize RF sensors 300, 302,
304 to a common network time in an embodiment in accordance with
the invention. Other embodiments in accordance with the invention
may implement different time synchronizing protocols. Moreover, the
network devices that add delay, such as, for example, a switch,
router, and repeater, may need symmetrical transmission and
reception delays in other embodiments in accordance with the
invention. In some of these embodiments, the delays may be
compensated for in the RF system calibrations when the mean of the
asymmetrical delays is stationary over a time interval.
[0019] The required accuracy in synchronizing RF sensors 300, 302,
304 depends on the application. More precise timing accuracy is
required in some applications, such as in geolocation applications.
For signal detection, the timing accuracy is determined by the
amount of memory in each device and the network latency. In other
embodiments in accordance with the invention, other types of
devices or systems may be used for the common network clock,
including, but not limited to, other networking timing protocols,
such as NTP, global positioning systems (GPS), high stability
internal clocks such as atomic clocks, or any other clock with
long-term stability compatible with the application.
[0020] Referring to FIG. 4, there is shown a flowchart of a method
for identifying one or more signal frequencies emitted at a known
location in an embodiment in accordance with the invention. The
method of FIG. 4 is performed in real-time in an embodiment in
accordance with the invention. Initially a location to examine is
selected, as shown in block 400. Because the locations of the RF
sensors are known, the distances between the RF sensors and the
selected location can be determined. Thus, the distance between
each RF sensor and the selected location is determined at block
402.
[0021] The expected power for each RF sensor is then determined, as
shown in block 404. The expected power for a sensor is determined
by the equation 1/(d).sup.2, where d is the distance between the
selected location and the RF sensor. Once the expected power has
been calculated for each RF sensor, the expected power difference
for each pair of sensors is calculated (block 406). The power
difference is determined by comparing 1/(d1).sup.2 with
1/(d2).sup.2 for sensor 1 and sensor 2 in each sensor pair in an
embodiment in accordance with the invention. By way of example
only, if sensor 1 is 1/4 the distance to the selected location and
sensor 2 is 3/4 the distance, the energy at sensor 1 for a
non-directional RF signal is expected to be 9 times greater than
the energy observed at sensor 2. In terms of power, a difference of
19.08 dB ((20 log(9))) is expected between sensor 1 and sensor
2.
[0022] RF data is then acquired by the RF sensors and a spectrum
trace of power versus frequency generated at block 408. Next, at
block 410, the observed power differences for the pairs of sensors
are compared with the expected power differences. A determination
is then made at block 412 as to whether the observed power
differences match or nearly match the expected power differences at
one or more particular frequencies. If so, each particular
frequency is determined to be a probable frequency for the RF
signal emitted at the known location. The frequency is a probable
frequency when the observed power differences match the expected
power differences, nearly match the expected power differences
within a given error range, or if there is more than one near match
in an embodiment in accordance with the invention.
[0023] The probable frequency or frequencies are then output, as
shown in block 414. The one or more probable frequencies are
displayed to a user in an embodiment in accordance with the
invention. In another embodiment in accordance with the invention,
a printed document listing the probable frequency or frequencies is
generated. And in yet another embodiment, the probable frequency or
frequencies are transmitted to the RF sensors in a network.
[0024] The method shown in FIG. 4 may be used for a variety of
purposes. By way of example only, law enforcement officials may
determine a person of interest resides at a particular address and
want to ascertain if any RF signals are emitted from that address.
The method of FIG. 4 is then used to determine the probable
frequency or frequencies emitted at that address. This allows the
law enforcement officials to then monitor the probable frequency or
frequencies emitted at that location. Monitoring of the frequencies
is performed by a network of RF sensors (FIG. 3) in an embodiment
in accordance with the invention.
[0025] Although FIG. 4 describes a method for identifying one or
more probable frequencies using power differences, embodiments in
accordance with the invention are not limited to this
implementation. Other embodiments in accordance with the invention
identify one or more probable frequencies emitted at a known
location using differences in other signal values, such as, for
example, differences in energy levels.
[0026] FIGS. 5A-5B depict a flowchart of a method for identifying
and monitoring one or more signal frequencies emitted at a known
location in an embodiment in accordance with the invention. The
method shown in FIGS. 5A-5B is performed after spectral traces are
generated by multiple RF sensors and stored in a central processing
device in an embodiment in accordance with the invention. Initially
multiple RF sensors each acquire RF data and generate a spectrum
trace of power versus frequency, as shown in block 500. The RF
sensors then transmit the spectral traces to a central processing
device (block 502) and the central processing device stores the
traces (block 504). The central processing device stores the traces
in a database or table in an embodiment in accordance with the
invention. The spectral data received from the sensors is
time-aligned spectral data because the RF sensors are all
synchronized to the common network clock in an embodiment in
accordance with the invention.
[0027] A location is then selected at block 506. The location is
selected some time after the traces are stored in the central
processing device in an embodiment in accordance with the
invention. The distance between each RF sensor and the selected
location is then determined at block 508. The expected power for
each RF sensor is also determined, as shown in block 510. Once the
expected power has been calculated for each RF sensor, the expected
power difference for each pair of sensors is calculated (block
512).
[0028] Next, at block 514, the observed power differences for the
pairs of sensors are compared with the expected power differences.
A determination is then made at block 516 as to whether the
observed power differences match or nearly match the expected power
differences at one or more particular frequencies. If so, each
particular frequency is determined to be a probable frequency for
the RF signal emitted at the known location. The frequency is a
probable frequency when the observed power differences match the
expected power differences, nearly match the expected power
differences within a given error range, or if there is more than
one near match in an embodiment in accordance with the
invention.
[0029] The probable frequency or frequencies are then output (block
518) and monitored at the selected location (block 520). The one or
more probable frequencies are displayed to a user in an embodiment
in accordance with the invention. In another embodiment in
accordance with the invention, a printed document listing the
probable frequency or frequencies is generated. And in yet another
embodiment, the probable frequency or frequencies are transmitted
to the RF sensors using the network.
[0030] The method shown in FIGS. 5A-5B may be used for a variety of
purposes. By way of example only, law enforcement officials may
determine a person of interest resides at a particular address
previously examined by a network of RF sensors. The method of FIGS.
5A-5B is used to determine which frequencies were previously
emitted at that address. This allows the law enforcement officials
to then presently monitor the probable frequency or frequencies
emitted at that location. Monitoring of the frequencies is
performed by a network of RF sensors (FIG. 3) in an embodiment in
accordance with the invention.
[0031] Although FIGS. 5A-5B describe a method for identifying one
or more probable frequencies using power differences, embodiments
in accordance with the invention are not limited to this
implementation. Other embodiments in accordance with the invention
identify one or more probable frequencies emitted at a known
location using differences in other signal values, such as, for
example, differences in energy levels.
[0032] The power differences can be compared at block 410 in FIG. 4
and at block 514 in FIG. 5B using one of several techniques. FIG.
6A is an illustration of a first table that may be used in block
410 of FIG. 4 and in block 514 of FIG. 5B. Table 600 records the
observed power levels (p.sub.1, p.sub.2, p.sub.3 . . . p.sub.12) at
various frequencies (f.sub.1, f.sub.2, f.sub.3 . . . f.sub.n) for
each sensor (S.sub.1, S.sub.2, S.sub.3). The observed power levels
are used to determine the power differences for pairs of sensors,
which are then compared with the expected power differences to
determine whether the observed power differences match or nearly
match the expected power differences at a particular frequency or
frequencies. In other embodiments in accordance with the invention,
table 600 records observed energy levels at various frequencies
(f.sub.1, f.sub.2, f.sub.3 . . . f.sub.n) for each sensor (S.sub.1,
S.sub.2, S.sub.3).
[0033] FIG. 6B is an illustration of a second table that may be
used in block 410 of FIG. 4 and in block 514 of FIG. 5B. Table 602
records the differences in power levels (d.sub.1, d.sub.2, d.sub.3
. . . d.sub.12) at various frequencies ((f.sub.1, f.sub.2, f.sub.3
. . . f.sub.n) for each sensor pair (SP.sub.1,2, SP.sub.1,3,
SP.sub.2,3). The observed power differences are then compared with
the expected power differences to determine whether the observed
power differences match or nearly match the expected power
differences at a particular frequency or frequencies. In other
embodiments in accordance with the invention, table 602 records
observed differences in energy levels at various frequencies
(f.sub.1, f.sub.2, f.sub.3 . . . f.sub.n) for each sensor (S.sub.1,
S.sub.2, S.sub.3).
[0034] And finally, FIG. 7 is a pictorial representation of two
traces of the power of an RF signal over a frequency spectrum that
may be used in block 410 of FIG. 4 and in block 514 of FIG. 5B. A
trace 700, 702 is generated for the RF data captured by each sensor
in an embodiment in accordance with the invention. Traces 700, 702
are then overlaid with each other in order to compare power
differences at various frequencies and determine whether the
observed power differences match or nearly match the expected power
differences for a particular frequency or frequencies. In FIG. 6,
traces 700, 702 are shown separately for the sake of clarity. In
other embodiments in accordance with the invention, traces of
signal amplitudes versus frequency are generated and used to
determine whether the observed energy differences match or nearly
match the expected energy differences for a particular frequency or
frequencies.
[0035] Although the descriptions of FIGS. 3-7 include the use of
three RF sensors, embodiments in accordance with the invention are
not limited to three sensors. Three or more RF sensors may be used
to identify one or more probable frequencies emitted at a known
location. Typically the confidence level associated with the
probable frequency or frequencies increases with the number of
sensors while the error associated with the probable frequency or
frequencies decreases.
* * * * *